This invention relates in general to main field coils for use in dynamoelectric machines and in particular to main field coils having air vents, for use with synchronous generators for A/C power generation. Typically the main field coils have been wound using multiple strands of small size wire connected in parallel. For ventilation and cooling purposes open areas or air vents are formed in the coil as the wire is wound. The air vents are formed by placing temporary or permanent spacers against the wiring and then winding more wire about the spacers. These types of field coils have several disadvantages. The use of multiple wires of a small size is very costly and the probability is very high that shorted turns will occur due to crossovers of the wire under winding pressure. Furthermore the resulting coil is not very rigid and may be subject to deformation. Because of the small wire size it is difficult to produce uniform field coils and the heat transfer characteristics of the coil is not very good due to the multiple layers of insulation.
The use of large size single solid wire such as round magnet wire has been utilized in the winding of main field coils. However it has been found impractical to form air vents in such coils due to the high winding tension which must be used to form the solid strand wire. This results in high winding temperatures when in use due to the lack of air vents. For the reasons given above it is more desirable to use a solid strand wire for the main field coil rather than multiple small strands of wire.